This invention relates generally to the portioning and packaging by weight of items normally sold in packages of fixed weights, and particularly to the portioning and packaging by weight of a plurality of articles of randomly differing weights, such as fruits and vegetables.
In any scheme of packaging food commodities into conveniently small packages of equal weight portions, the packager wants ideally to have each portion conform exactly to the desired package label weight. To abide by consumer protection laws, the packager must insure that each package contains at least the stated label weight. While any weight in excess of this required minimum is of no concern to the authorities, it is of prime concern to the packager as it represents a serious loss of profit. To portion exactly to the minimum weight, however, is impractical, as it would require too much weighing, calculating, portion adjustment, and individualized effort, and thus is too costly.
Over the years, packagers have well advanced the art of rapid packaging, particularly with regard to combating weight variation error sources such as scale inaccuracies, product feed control, moisture shrinkage, density variations, package tare weight variation, and the like. To a large degree, packagers of granular and liquid items have been quite successful in improving these arts, frequently achieving efficient production speeds while maintaining long term average overweight losses of less than one percent of the package label weight. Packagers of weight portioned discrete individual articles, such as fruits and vegetables, have not equally benefited, however, from such advancements in the art.
In the weight portioning of discrete articles of varying and variable individual weights, such as fruits and vegetables, an additional error source overshadows the aforementioned considerations. With such items, even though harvested ripe from one particular field or farm, and thus afforded equal growing opportunity, it is common to observe weight variations among the individual articles ranging as high as eight to one. The most usual method of weight portioning such items is by feed mechanisms intended to dispense the last few articles sequentially, one-at-a-time, into a container residing on a scale. The scale is set at a target weight setting, usually equal to the required minimum portion weight plus an allowance for one or more of the known error sources, and halts the feeding of articles into the container as soon as a final article causes the weight to equal or exceed the target weight setting of the scale. Owing to the randomly highly variable individual weights of the articles progressing through the feed mechanism, the group weight of the portion being collected is highly variable just prior to the addition of the final portion-completing article. Also, the individual weight of the final article is equally unknown and variable. These two combine, even in mechanisms that precisely limit the feeding of articles to one-at-a-time, to provide an uncontrolled varying overweight that can range upward to almost the weight of the final article itself. While the occasional group may complete at just precisely the required minimum target weight, the long term average of such portionings are observed to be overweight by a substantial fraction of the average weight of one article.
With the increasing trend toward smaller packaged portions by weight, brought about by demands of consumer convenience, the serious nature of this overweight loss can better be appreciated. It is not uncommon today to package fruits and vegetables to weight portions resulting in as few as five or six discrete articles. With these packages, long term average overweights are commonly ten percent or more in excess of the minimum package label weight, sharply contrasting with the fractional percent associated with granular or liquid items. Various systems have been proposed to combat this problem. In general, these schemes involve some initial separation process to reserve the smallest size articles for final topping use; the rejection and repackaging of portions underweight or excessively overweight; the pre-classification by weight for the purpose of achieving overweight reduction by counted combinations; and others. These schemes have variously failed, or proved of limited economic benefit, due to many reasons, including limited availability of small topping articles within the parent supply, lost packaging materials and production speed, cumulative inaccuracies of multiple weighings, difficulties in insuring that articles of all weights are promptly packed, complexity and expense of apparatus, and like reasons. Therefore, there now exists a demand for a method of portioning and packaging items such as fruits and vegetables much more accurately.
Accordingly, it is an object of this invention to provide an accurate method for weight portioning and packaging items of varying and variable individual weights such as fruits and vegetables. It is a further object of this invention to provide a method which will insure the prompt packaging of all articles contained within a parent large bulk supply of variable weight articles, including those articles which are very large or very small. While it is not an object of this invention to advance the art of controlling previously mentioned sources of overweight errors common to the portioning of granular and discrete items alike, it may well be that my teachings will be applicable in some way to that field also.